Ultrasound Imaging System

ABSTRACT

An ultrasound imaging system ( 100 ). An exemplary system ( 100 ) includes a plurality of transducer elements ( 136 ) formed in subarrays ( 140 ) and a plurality of subarray circuit units ( 160 ′), with each circuit unit ( 160 ′) connected to a subarray ( 140 ) of the transducer elements ( 136 ). The circuitry in each unit ( 160 ′) comprises a plurality of integrated circuits ( 330, 340, 350 ), with at least a first ( 340 ) of the integrated circuits formed over a second ( 330 ) of the integrated circuits in a stacked configuration. In an example illustration the first integrated circuit ( 340 ) includes a first plurality of first bond pads ( 345 ) along a surface ( 342 ) thereof and the second integrated circuit ( 330 ) includes a second plurality of second bond pads ( 335 ) along a surface ( 331 ) thereof, with bond wires ( 344 ) extending between pairs of first and second bond pads to provide input/output signal connections therebetween.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to ultrasound imaging systems and, moreparticularly, to systems having beamforming electronics.

2. Background Art

Real time 3D ultrasound imaging for medical applications requireshousing an array of perhaps several thousand transducer elements andassociated signal processing electronics in a hand-held probe unit. Insmaller systems (e.g., having only a few hundred array elements) it hasbeen conventional to carry the transducer signals through a multi-wirecable to a system console containing essentially all of the processingcircuitry for image generation. However, with larger arrays containingtransducer elements numbering in the thousands, or in the tens ofthousands or even more, it is difficult and impractical to perform allof the signal processing in a remote unit. This would require dedicatedleads, each forming a separate connection between a transducer elementand processing circuitry located in the console. To address thisproblem, a limited portion of the processing circuitry has been placedin the probe. For example, a large array of transducer elements may bedivided into subarrays of uniform size, e.g., ranging from 10 to 40transducer elements, with a dedicated unit of beam forming andprocessing circuitry for each subarray, herein referred as a subarraycircuit unit. Each subarray circuit unit can combine the signalsgenerated by all of the transducer elements in the subarray into asingle channel or wire, e.g., by analog beam-formation. With this orother configurations, the signals received from all of the elements inthe array can be transferred via a reduced number of cable leads to theprocessing circuitry in the console. In this way the thousands ofsignals can be transferred while retaining a manageable cable size.

To effect circuit functions in the probe, each subarray circuit unitnormally includes high voltage transmitter circuitry, low voltagereceiver circuitry and digital control circuitry. Implementation ofthese different circuit functions has required fabrication of multipleintegrated circuits, e.g., Application Specific Integrated Circuits(ASICs), because the differing circuit functions have required differentsemiconductor manufacturing processes. The multiple ASIC componentsrequired for all of the subarray circuits have consumed a relativelylarge volume of available space in the probe unit. With theimpracticality of fabricating all three functions in one monolithic die,the volume required for housing these subarray circuit units can be afactor limiting the practical size of a transducer array housed in ahand-held probe unit. Size and weight considerations influence the easewith which the hand-held probe unit can be maneuvered during examinationprocedures.

The need to reduce size and weight of probe units and consoles isespecially relevant to portable ultrasound imaging systems which may beconfigured with note-book computer systems. Generally, size and weightare constraining factors which can limit achievable image quality ofsystems which use portable, hand-held probe units. Consequently, manyhand-held probe units employ a relatively low number of transducerelements in order to minimize the amount of wiring and circuitry andthereby meet these criteria. Yet it is recognized that improved imagequality can increase the diagnostic utility of these systems.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment an ultrasound imaging system includes an array oftransducer elements formed in a matrix of subarrays, with each subarraycontaining a plurality of the transducer elements. Each subarray oftransducer elements connected to a circuit unit, with circuitry in eachunit including two or more integrated circuits in a stackedconfiguration, with each unit including transmission circuitry forgenerating acoustic signals, receiver circuitry for processing reflectedsignals and control circuitry. A system console is coupled to receiveimage information from the circuit units and includes image processingcircuitry for displaying an image. All of the subarrays are positionedalong a first plane, a first of the integrated circuits is positioned ina second plane parallel with the first plane and a second of theintegrated circuits is positioned in a third plane parallel with thefirst plane.

In another embodiment, an ultrasound imaging system includes transducerelements formed in adjoining subarrays and subarray circuit units, eachcircuit unit being connected to a subarray of the transducer elements.Circuitry in each unit includes a plurality of integrated circuits, withat least a first of the integrated circuits formed over a second of theintegrated circuits in a stacked configuration. A plurality of circuitboard structures provide electrical connections between the transducerelements and the subarray circuit units. For at least one of the circuitunits, the first integrated circuit includes a first plurality of firstbond pads along a surface thereof and the second integrated circuitincludes a second plurality of second bond pads along a surface thereof,and bond wires extend between pairs of first and second bond pads toprovide input/output signal connections therebetween.

In still another embodiment, an ultrasound imaging system includes atransducer array probe unit and a system console for processing anddisplaying image data. The probe unit includes an array of transducerelements arranged in a matrix of subarrays, with each subarraycontaining a plurality of the transducer elements. A plurality ofsubarray circuit units each include multiple integrated circuits formedover one another in a stacked configuration. Each circuit unit isconnected to one of the subarrays of transducer elements. A multi-wiringunit provides electrical connection between subarrays of transducerelements and subarrays of circuit units and provides input/output signalconnections between at least the one subarray circuit unit and thesystem console. A plurality of removable clamps provide connectionsbetween one or more flexible circuits and the circuit board. A first ofthe integrated circuits is positioned in a first plane and a second ofthe integrated circuits is positioned in a second plane parallel withthe first plane, with the first integrated circuit including a pluralityof bond pads formed along a surface thereof, with the circuit unitincluding bond wires extending from some of the bond pads on the firstintegrated circuit to the second circuit to provide connections betweenthe first and second integrated circuits.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood when the followingdescription is read in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a simplified schematic diagram of an ultrasound imagingsystem;

FIG. 2 provides a cross-sectional view of exemplary transducer andmulti-chip module circuitry which may be formed in the system of FIG. 1;

FIG. 3 provides a cross-sectional view of another example of transducerand multi-chip module circuitry which may be formed in the system ofFIG. 1;

FIG. 4 is a cross-sectional view of an exemplary probe unit suitable forincorporation in the system of FIG. 1;

FIG. 5 is a cross-sectional view illustrating a multi-chip module in theprobe unit of FIG. 4;

FIG. 6 is a cross-sectional view further illustrating features of theprobe unit shown in FIG. 4;

FIG. 7 is a cross-sectional view further illustrating features of theprobe unit shown in FIG. 4; and

FIG. 8 illustrates an ultrasound imaging system according to anembodiment of the invention.

Like reference numbers are used throughout the figures to indicate likefeatures. Individual features in the figures may not be drawn to scale.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 provides a partial view of an exemplary ultrasound imaging system100 including a system console 110, a display 120 and a large areatransducer array probe unit 130. The probe unit houses one hundredtwenty eight subarray circuit units 160, sequentially referenced as160-1 through 160-128. The probe unit 130 may be of the hand-held type.Information is transferred between the probe unit 130 and the systemconsole 110 via a multi-wire cable 132 comprising one hundredtwenty-eight signal lines 133. Each signal line 133 is coupled between aline connector 115 in the system console 110 and a line connector 135 inthe probe unit 130. The console 110 receives image information from thesubarray circuit units 160 through the signal lines 133 for processingby electronics including a system controller 112 coupled to primarybeamforming circuitry 114 and a scan converter 116. The controller 112is also coupled to the subarray circuit units 160 in the probe 130,providing overall control of the system 100. The primary beamformingcircuitry 114 processes electrical signals received from individualsubarray circuit units 160 to produce sector scan signals. The scanconverter 116 having image processing circuitry converts the sector scansignals to raster signals suitable for image presentation on the display120.

Referring also to FIG. 2, the probe unit 130 includes a two-dimensionallinear array 134 of transducer elements 136 connected to the subarraycircuit units 160 through an interface formed with a multi-wiring unit143. The exemplary transducer array 134 includes four thousandninety-six transducer elements 136 arranged in a matrix of one hundredtwenty-eight subarrays 140. Each subarray 140 has thirty-two transducerelements 136 arranged along four rows 141 and eight columns 142.Exemplary columns 142 of elements 136 are shown in FIG. 1 with phantomlines indicating groups of eight columns in a subarray 140. Fouradjoining rows 141 of elements 136 are shown in FIG. 2, thesecorresponding to rows of one subarray 140. In this example, rows 141 andcolumns 142 are formed in orthogonal directions along a plane P11.

During operation each transducer element 136 in a subarray 140 transmitsultrasonic signals to and receives reflected ultrasonic signals from asubject, e.g., a patient undergoing examination. Each subarray circuitunit 160 comprises a transmitter ASIC 230, having circuitry forgenerating pulse signals and sending to the transducer element subarray140; a receiver ASIC 240, having circuitry for processing of thereflected signals received from the transducer elements 136; and acontroller ASIC 250 having transmit control circuitry for pulse timing.In each circuit unit 160, the controller ASIC 250 is formed over thereceiver ASIC 240 which is formed over the transmitter ASIC 230, in astacked configuration 170, also referred to herein as a multi-chipmodule 170. The specific order of stacking of the ASICs is variable andthe example embodiment shown is one of multiple possible configurations.Also, the exemplary system partitioning of functionality between theASICs 230, 240 and 250 is merely illustrative while there are numerousother possible groupings of transmitter, receiver, and control circuitryamong various ASIC designs and various layers in the multi-chip module.The configuration of the multi-chip module 170 substantially reduces thesize of the subarray circuit units 160 relative to systems having eachof multiple integrated circuits positioned in the same plane forconnection to a substrate, e.g., using a ball grid array.

In the multi-chip module 170 parasitic capacitance associated withelectrical connections between ASIC devices within the unit 160 issignificantly reduced because many of the bond wires effect relativelyshort distance connections which would otherwise be made with relativelylong electrical traces formed in circuit boards.

As illustrated in FIG. 1, each controller ASIC 250 receives 64 signalsfrom the system controller 112 along lines 137 and sends 64 transmitsignals to the transmitter ASIC 230 along lines 257 in the multi-chipmodule 170. In response to a transmit signal, a transmitter ASIC 230generates and sends 32 pulse signals to the transducer subarray 140.Each pulse signal travels along one of 32 individual lines 231 so thateach transducer element 136 can receive a different pulse signal and,together, the elements in the array synthesize an acoustic signal ofdesired characteristics which propagates to an object under study.Elements in each subarray 140 then absorb energy of signals reflectedfrom the subject, and the transmitter ASICs 230 receive electricalsignals indicative thereof from the subarray 140 along one of the 32individual lines 231. This signal information is transferred from theASIC 230 to the receiver ASIC 240 along 32 individual lines 237 whereininformation on the 32 lines is combined on to a single channel subarraysignal line 247. In this manner, the number of signal lines in the cable132 can be significantly reduced.

FIG. 2 illustrates connection of the ASICs 230, 240 and 250 in asubarray circuit unit 160 and connection to transducer element 136 in anassociated subarray 140, having an upper surface 291 and a lower surface292, via the multi-wiring unit 143. In this example, the multi-wiringunit 143 is a Flexible Circuit Board (FCB) 270 having a plurality ofupper FCB traces 273, e.g., 273 a, 273 b, etc., formed along an uppersurface 271 and a plurality of lower FCB contact pads 277 formed along alower surface 272. A solder bump 278 is formed on each lower FCB contactpad 277. Adjacent transducer subarrays 140 of transducer elements 136extend along the plane P11 defining, for purposes of orientation,horizontal directions such that a vertical orientation is normal to theplane P11 and upper and lower positions are relative to a horizontaldirection.

In the multi-chip module 170, having an upper surface 171 and a lowersurface 172, the controller ASIC 250 has a plurality of controller ASICbond pads 255 along an upper surface 252 thereof, and the receiver ASIC240 has a plurality of receiver ASIC bond pads 245 along an uppersurface 242 thereof, and the transmitter ASIC 230 has a plurality oftransmitter ASIC bond pads 235 along an upper surface 232 thereof. TheASIC 230 is formed on a routing substrate 220 having an upper surface227, a lower surface 228, a plurality of substrate bond pads 225 (e.g.,225 a, 225 b and 225 c) and a plurality of substrate vias 226. Thesubstrate 220 comprises a layer 221 of insulative material, e.g., apolyimide resin film, laminated with conductive layers formed of copperor aluminum along the upper and lower surfaces 227 and 228, which arepatterned and etched to form upper conductive traces 222 and lowerconductive traces 224.

A plurality of controller ASIC bonding wires 254, receiver ASIC bondwires 244, and transmitter ASIC bond wires 234 provide electricalconnections between the ASICs within each multi-chip module 170. Inother embodiments, a heat spreader may be provided along the uppersurface 171 of the multi-chip module 170 for enhancing heat removal fromthe package.

The controller ASIC bonding wires 254 electrically connect thecontroller ASIC bonding pads 255 to a first group 225 a of the substratebonding pads 225 on the routing substrate 220. The receiver ASIC bondingwires 244 electrically connect the receiver ASIC bonding pads 245 to asecond group 225 b of the substrate bonding pads 225 and the transmitterASIC bonding wires 234 electrically connect the transmitter ASIC bondingpads 235 to a third group 225 c of the substrate bonding pads 225. Thesubstrate bonding pads 225 are connected to the patterned upper traces222 for routing. Through vias 226, i.e., plated-through holes, in therouting substrate 220 electrically connect the upper traces 222 to thelower traces 224. Input/output (I/O) solder balls 229 formed on thelower traces 224 effect electrical connections between the multi-chipmodule 170 and the FCB 270 of the multi-wiring unit 143. The transmitterASIC 230 is positioned in a second plane P12 parallel to and above theplane P11 for attachment to the upper surface 227 of the substrate 220with a first adhesive layer 260. The receiver ASIC 240 is positioned ina third plane P13 parallel to and above the second plane P12 forattachment to the transmitter ASIC 230 with a second adhesive layer 262.The controller ASIC 250 is positioned in a fourth plane P14 above andparallel to the plane P13 for attachment to the receiver ASIC by a thirdadhesive layer 264. An insulative plastic mold cap 265 protectivelyencapsulates the ASICs 230, 240, and 250, the bond pads 235, 245, and255, the bonding wires 234, 244, and 254, and the upper surface 227 ofthe substrate 220.

Individual transducer elements 136 each comprise a matching layer 295formed against a piezoelectric material layer 296. The matching layer295 provides suitable acoustic characteristics for transmitting acousticenergy to, and receiving acoustic signals from, the subject under study.The piezoelectric material layer 296 is formed over a lower or rearelectrode 297 which is connected through a transducer contact pad 293and a solder bump 278 to the multi-wiring unit 143. The rear electrode297, the matching layer 295, and the piezoelectric material layer 296 ineach transducer element are electrically isolated from like componentsof other transducer elements by a series of spaces or kerfs 299 whichmay be created by parallel sawing to create individual ones of thetransducer components 296 and rear electrodes 297. A front electrode298, typically formed of a relatively thin conductive material, isdeposited over the matching layers 295 of elements 136 in the entiresubarray 140 of transducer elements, providing a common ground for thesubarray 140.

The transducer elements 136 may further include a dematching layer (notshown) or a backing layer having suitable acoustic characteristics toabsorb or scatter acoustic energy transmitted in the direction away froman object under study. This prevents the acoustic energy from beingreflected from structures or interfaces behind the transducer elementsand back into the piezoelectric material. The acoustic backing materialmay consist of a composite of metal particles (e.g., tungsten) in anattenuating soft material such as rubber, epoxy or plastic. Otheracoustic backing material compositions may also be used. The transducerelements may, for example, be lead zirconate titanate transducers(PZTs), capacitive Micromachined Ultrasonic Transducers (cMUTs),piezoelectric micromachined Ultrasonic Transducers (pMUTs), orPolyVinylidine DiFluoride (PVDF) transducers.

With each solder bump 278 formed on a lower FCB contact pad 277, aplurality of electrically conductive through-flex vias 276, extend fromthe upper surface 271 to the lower surface 272 of the FCB 270, and afirst group 273 a of the upper FCB traces 273 provide electricalconnections between each transducer element 136 in the subarray 140 andthe corresponding upper conductive trace 222. The upper trace 222 isconnected to the transmitter ASIC 230 via the substrate bond pad 225 cand the transmitter ASIC bond wire 234 connected to the transmitter ASICbond pad 235. A second group 273 b of the upper FCB traces 273 providesI/O connections (not shown) between the multi-chip module 170 andelectronics in the system console. The multi-chip module 170 is attachedto the upper surface 271 of the FCB 270 with a dielectric adhesive 275.The FCB 270, positioned along a fifth plane P15 parallel to the firstplane P11, is attached along the upper surface 291 of each transducersubarray 140 with a dielectric adhesive 280. The FCB 270 may also serveas a dematching layer. In other embodiments, more than one flexiblecircuit board may form the multi-wiring unit 143 for I/O connections,and an additional dematching layer may be provided between themulti-chip module 170 and the FCB 270 or between the FCB 270 and thetransducer subarrays 140.

Along the plane in which the view of FIG. 2 is taken, the lateraldimension a₁, as measured along the lower surface 172 of the multi-chipmodule 170, is less than or equal to the lateral dimension a₂, measuredalong the lower surface 292 of the transducer subarray 140. This enablesformation of a large matrix of subarrays 140 without having asubstantial gap between adjacent subarrays 140.

FIG. 3 illustrates a second multi-chip module 170′ wherein a pluralityof subarray circuit units 160′, in lieu of the circuit units 160, areeach connected to the transducer element subarray 140 via themulti-wiring unit 143 as described with respect to FIG. 2 with adjacenttransducer subarrays 140 of transducer elements 136 extending along theplane P11.

Each multi-chip module 170′, having upper and lower surfaces 171′, 172′,includes a series of ASICs in a stacked configuration. A controller ASIC350, having a plurality of bond pads 355 formed along an upper surface352 thereof, is formed over a receiver ASIC 340, having a plurality ofbond pads 345 formed along an upper surface 342 thereof, which is formedover a transmitter ASIC 330 having a plurality of bond pads 335 formedalong an upper surface 331 thereof. The transmitter ASIC 330 furtherincludes a plurality of through-die vias 336, and a plurality of contactpads 338 formed along a lower surface 332. In this example, the ASIC330, the lower-most of the three ASIC die in the multi-chip module 170′,serves as a routing substrate for circuitry on the controller ASIC 350and the receiver ASIC 340. A plurality of controller ASIC bonding wires354 and a plurality of receiver ASIC bonding wires 344 extend from theASIC 330 to provide electrical connections among the three ASICs in themulti-chip module 170′.

The controller ASIC bonding wires 354 electrically connect thecontroller ASIC bonding pads 355 to a first group 335 a of transmitterASIC bonding pads 335. The receiver ASIC bonding wires 344 electricallyconnect the receiver ASIC bonding pads 345 to a second group 335 b ofthe transmitter ASIC bonding pads 335. Routing among ASICs is providedvia a metallization structure (not shown) within the transmitter ASICdie 330. The transmitter ASIC bonding pads 335 are connected to thethrough-die vias 336, which may be filled with conductive material suchas copper or aluminum, via upper traces 337 formed along the uppersurface 331. The through-die vias 336 electrically connect the bond pads335 to the contact pads 338 formed along the lower surface 172′.Input/output (I/O) solder balls 339 are formed on the contact pads 338for I/O connections. Accordingly, the ASICs 330, 340, and 350 areelectrically connected to the solder balls 339. The transmitter ASIC 330having wiring patterns or traces 337 is positioned in a second plane P22parallel to the plane P11 and attached to the upper surface of the FCB270 with a dielectric adhesive layer 375. The receiver ASIC 340 ispositioned along a third plane P23 parallel to the second plane P22 andis attached to, and vertically spaced from, the transmitter ASIC 330with an adhesive layer 362. The controller ASIC 350 is positioned alonga fourth plane P24 also parallel to the second plane P22 and is attachedto the receiver ASIC 340 with another adhesive layer 364. An insulativeplastic mold cap 365 protectively encapsulates the ASICs 340 and 350,the bonding wires 344 and 354, the bond pads 335, 345 and 355, and theupper surface 331 of the transmitter ASIC 330.

In the plane along which the view of FIG. 3 is taken, the lateraldimension a₁ of the multi-chip module 170′, taken along the lowersurface 172′, is less than or equal to the lateral dimension a₂ of thetransducer subarray 140, taken along the lower surface 292′. Thisenables formation of a large matrix of subarrays 140 without asubstantial gap between the adjacent subarrays 140.

According to another embodiment, FIG. 4 illustrates in a partialcross-sectional view a probe unit 410 for the system 100 comprising aplurality of the multi-chip modules 170′ as described with reference toFIG. 3. The probe 410 comprises a two-dimensional array 412 oftransducer elements 413, a plurality of flexible circuits 420 or flexeshaving electrical traces (not shown), and a plurality of Printed CircuitBoards (PCBs) 440 each having one or more multi-chip modules 170′. Thetransducer elements 413 are arranged in a plurality of subarrays 415,each subarray 415 comprising one row of transducer elements 413. Eachsubarray 415 is coupled to a flex circuit 420 for connection to acorresponding multi-chip module 170′. The flexes 420 are separated fromeach other by a non-conducting spacer 430 formed of material such asepoxy. Each flex 420 is joined to a corresponding PCB 440 by one or moreremovable clamps 480. A plurality of flexible connectors 465 connectsthe PCBs 440 with a probe line connector 460. A cable bundle 470 couplesthe probe line connector 460 to a system line 472 in order to transfersignals between the multi-chip modules 170′ and an electronic componentssuch as the main beamformer 114 illustrated in FIG. 1.

Connection of the flexes 420 to the PCB's 440 by clamps 480 allows forseparate fabrication and assembly of components. Thus, the transducerarray 412 may be conventionally fabricated under low temperatureconditions and assembled with the flexes 420 in a process which isseparate and isolated from the relatively high temperature assembly ofcomponents which form the PCB's 440. The multi-chip modules 170′ can bemounted onto the PCBs 440 at a temperature greater than 250 C in areflow oven without exposing the transducers 415 to high temperatureconditions. Also, with separate and isolated processes, the transducerarray 412 can undergo physical processing, such as sawing and grindingoperations, without exposing sensitive components in the PCB 440 tocontaminants. Otherwise, electrically conductive particles generatedduring grinding operations could cause shorts in the PCB components. Theclamp connection effects assembly of flexes 420 and PCBs 440 after thetransducer array 412 is fabricated in isolation from steps relating tofabrication and assembly of the PCB components. Thus fabrication stepsfor each component can be optimized without concern that anothercomponent may be degraded. Each flex 420 can be coupled to acorresponding PCB with mating connectors, an anisotropically conductivefilm, bump bonding or hot bar bonding. When clamp connections or themating connectors are employed, the flex 420 and the PCB 440 can bereadily and repeatedly coupled and decoupled. This facilitates repair ofthe probe unit 410 when failures occur in either the transducer array412 or the PCB 440, allowing for replacement of defective componentswithout discarding the other components.

FIG. 5 illustrates for the system 100 exemplary electrical connectionsbetween the multi-chip module 170′ (illustrated in FIG. 3) and one ofthe PCBs 440 shown in FIG. 4. With each multi-chip module 170′ includingcontroller ASIC 350 positioned over a receiver ASIC 340 positioned overa transmitter ASIC 330, a plurality of contact pads 338 are formed alongthe lower surface 332 of the transmitter ASIC. Input/output (I/O) solderballs 339 are formed on the contact pads 338 for I/O connections. Thetransmitter ASIC bonding pads 335 are connected to the through-die vias336 by the upper traces 337. The PCB 440 having an upper surface 441 anda lower surface 442, comprises three adjoining dielectric layers 445,447 and 448. PCB contact pads 443 are formed along the upper surface 441providing connection between I/O solder balls 339 and upper level vias444, formed in the upper level dielectric layer 445. The vias 444contact underlying inner conductors 446 formed in the intra-leveldielectric 447. The transmitter ASIC 330 is attached to the uppersurface 441 of the PCB 440 with a dielectric adhesive layer 475. The PCB440 provides electrical connection between the transducer subarrays 415and the multi-chip modules 170′ and also provides electrical connectionbetween the multi-chip modules 170′ and electronics in the systemconsole 110 shown in FIG. 1.

An exemplary electrical connection between a PCB 440 and a flex 420 withone or more clamps 480 is illustrated in the partial cross-sectionalview of FIG. 6. As described with respect to FIG. 6, the PCB 440includes an upper surface 441, a lower surface 442, and three adjoiningdielectric layers: upper layer 445, intra-level layer 447 and lowerlayer 448. One or more contact pads 443 are formed along the uppersurface 441, and upper level vias 444 are formed in the upper leveldielectric layer 445. Underlying inner conductors 446 are formed in theintra-level dielectric 447. A plurality of gold bumps 449 are formed onthe PCB contact pads 443. The flex 420, having an upper surface 421 anda lower surface 422 includes flex contact pads 423 formed along thelower surface 422. For simplicity of illustration, only two PCB contactpads 443 and two flex contact pads 423 are shown in FIG. 6. One or moreholes are provided in the flex 420 and in the PCB 440 for clamping. Eachclamp 480 comprises a connecting bolt 482, a pair of washers 484 and apair of nuts 486. After clamping holes of the flex 420 are aligned withclamping holes of the PCB 440, the clamp bolts 482 are inserted andsecured with washers 484 and nuts 486. The clamping pressure effectselectrical contacts between the gold bumps 449, the flex contact pads423 and the PCB contact pads 443. Alternately, the flex contact pads 423and the PCB contact pads 443 may be bonded together by compression. Thebonding may be effected by gold plating of the contact pads 423 and 443prior to compression.

In an embodiment shown in the partial cross-sectional view of FIG. 7,electrical connection between the flexes 420 and the PCBs 440 is alsoeffected by clamping. Two PCBs 440 a and 440 b and four flexes 420 a,420 a′, 420 b and 420 b′ are joined by one or more clamps 480′. Thefirst PCB 440 a is coupled to the first and second flexes 420 a and 420a′ and the second PCB 440 b is coupled to the third and fourth flexes420 b and 420 b′. In other embodiments, more than two flexes 420 may becoupled to a PCB 440.

The first flex 420 a having an upper surface 421 a and a lower surface422 a, has two flex contact pads 423 a formed along the lower surface422 a, herein referred as first flex lower contact pads 423 a. Thesecond flex 420 a′ having an upper surface 421 a′ and a lower surface422 a′, has two flex contact pads 425 a′ formed along the upper surface421 a′, herein referred as second flex upper contact pads 425 a′. Fourflex contact pads 423 a′ are formed along the lower surface 422 a′. Thesecond flex 420 a′ further includes two through-flex vias 424 a whichprovide connection between the second flex upper contact pads 425 a′ andthe second flex lower contact pads 423 a′. Each of the lower contactpads 423 a of the first flex 420 a is coupled to a corresponding flextrace (not shown) of the first flex 420 a and each of the lower contactpads 423 a′ of the second flex 420 a′ is coupled to a corresponding flextrace (not shown) of the second flex 420 a′. The third flex 420 b havingan upper surface 421 b and a lower surface 422 b, has four upper flexcontact pads 425 b formed along the upper surface 421 b, and two lowerflex contact pads 423 b formed along the lower surface 422 b. The thirdflex 420 b further includes two through-flex vias 424 b which provideconnection between the third flex upper contact pads 425 b and the thirdflex lower contact pads 423 b. The fourth flex 420 b′ having an uppersurface 421 b′ and a lower surface 422 b′, has two upper flex contactpads 425 b′ formed along the upper surface 421 b′. Each upper contactpad 425 b of the third flex 420 b is coupled to a corresponding flextrace (not shown) of the third flex 420 b and each upper contact pad 425b′ of the fourth flex 420 b′ is coupled to a corresponding flex trace(not shown) of the fourth flex 420 b′. One or more holes (not shown) areprovided in the flexes 420 for clamping.

The first PCB 440 a having an upper surface 441 a and a lower surface442 a, includes PCB first contact pads 443 a formed along the uppersurface 441 a, upper level vias 444 a formed in an upper leveldielectric layer 445 a, underlying inner conductors 446 a formed in anintra-level dielectric 447 a, and a layer of dielectric 448 a. Thesecond PCB 440 b, having an upper surface 441 b and a lower surface 442b, includes second PCB contact pads 443 b formed along the lower surface442 b, lower level vias 444 b formed in a lower level dielectric layer445 b, underlying inner conductors 446 b formed in an intra-leveldielectric 447 b, and an overlying layer of dielectric 448 b. One ormore holes (not shown) are provided in the PCBs 440 for clamping. Eachclamp 480′ comprises a connecting bolt 482′, a pair of washers 484′ anda pair of nuts 486′. A plurality of gold bumps 426 (e.g., 426 a, 426 b)are formed on the second flex upper contact pads 425 a′ and the fourthflex upper contact pads 425 b′. A plurality of gold bumps 449 (e.g., 449a, 449 b) are formed on the first PCB contact pads 443 a and on thesecond PCB contact pads 443 b. After the clamping holes of the flexes420 and the PCBs 440 are aligned, the clamp bolts 482′ are inserted andsecured with washers 484′ and nuts 486′. The clamping pressure effectselectrical contacts between gold bumps 426, 449 and flex contact pads423. In other embodiments, the flexes 420 may be attached to semi-rigidFlexible Circuit Boards (FCBs) having one or more multi-chip modules. Instill other embodiments, the multi-chip modules 440 may be mounteddirectly onto the flex circuits 420.

FIG. 8 illustrates another embodiment comprising multi-chip modules 170′in an ultrasound imaging system 200. The exemplary ultrasound imagingsystem 200 includes a system console 110′, a display 120 and atransducer array probe 130′. In FIG. 8 the multi-chip modules 170′ areplaced in the system console 110′. The probe 130′ comprises an array134′ of transducer elements 136′. The transducer elements 136′ arearranged in a plurality of subarrays 140′, each subarray 140′ comprisingone row of transducer elements 136′. Information is transferred betweenthe probe 130′ and the system console 110′ via a multi-wire cable 132.Each wire 133 in the cable 132 is coupled to the system console 110′ andto the probe 130′ by a system line connector 115 and a probe lineconnector 135, respectively. A flexible circuit 137′ connects a subarray140′ of transducer elements 136′ to a corresponding probe line connector135. The console 110′ includes a system controller 112 coupled toprimary beamforming circuitry 114, a scan converter 116, and a pluralityof multi-chip modules 170′ having transmission circuitry, receivercircuitry, and controller circuitry. The multi-chip modules 170′ aremounted on a PCB 180. The system controller 112 may directly providetiming signals to transmission circuitry in the multi-chip module 170′which eliminates the need for controller circuitry in the multi-chipmodule 170′. The primary beamformer 114 receives electrical signals fromindividual multi-chip modules 170′ and processes the signals to producesector scan signals. The scan converter 116 converts the sector scansignals to raster display signals suitable for presentation on thedisplay 120.

Embodiments of multi-chip modules 170 in an ultrasound imaging systemhave been described. The multi-chip modules 170 may be directly coupledto a subarray 140 of transducers 142. The modules 170 may be coupled viaflexible circuits 420 and PCBs 440 in a probe 410 as illustrated in FIG.4. The modules 170 may be mounted on a PCB in a system console 110 asshown in FIG. 8. Each multi-chip module can comprise a series of stackedintegrated circuit die, e.g., formed by stacking a controller ASIC, areceiver ASIC, and a transmitter ASIC. The multi-chip module may alsocomprise beamformer circuitry. Multi-chip module configurations providea significant reduction in volumetric space requirements of a subarraycircuit unit 160. This enables tiling of relatively dense subarrays 140to form a high density relatively large area transducer array in ahand-held probe. The multi-chip module configuration provides areduction in size and an improvement in performance, e.g., reducedparasitic capacitance.

While several embodiments of the invention have been illustrated anddescribed, the invention is not so limited. Numerous modifications,variations, substitutions and equivalents will occur to those skilled inthe art without departing from the spirit and scope of the presentinvention as described in the claims.

1. An ultrasound imaging system of the type which generates an image ofan object under observation, comprising: an array of transducer elementsarranged along a plane in a matrix of subarrays, with each sub arraycontaining a plurality of the transducer elements, for generatingacoustic signals and receiving reflections of the signals; a pluralityof circuit units, each subarray of transducer elements connected to adifferent circuit unit, circuitry in each unit comprising two or moreintegrated circuits in a stacked configuration, with each unit includingtransmission circuitry for generating the acoustic signals, receivercircuitry for processing of the reflected signals and control circuitry;and a system console coupled to receive image information from thecircuit units and including image processing circuitry for displaying animage of the object, wherein all of the subarrays are positioned along afirst plane, a first of the integrated circuits is positioned in asecond plane parallel with the first plane and a second of theintegrated circuits is positioned in a third plane parallel with thefirst plane.
 2. The system of claim 1 further including a multi-wiringunit providing electrical connection between ones of the subarrays oftransducer elements and ones of the subarray circuit units, andproviding input/output signal connections between the one subarraycircuit unit and a multi-wire cable for connection to the systemconsole.
 3. The system of claim 2 wherein the multi-wiring unit includesone or more flexible circuit boards having a plurality of electricallyconductive through-flex vias.
 4. The system of claim 2 wherein eachsubarray is a two dimensional array such that the entire array oftransducer elements is arranged in rows and columns of elements andwherein the multi-wiring unit is positioned in a fourth plane parallelwith the first plane.
 5. The system of claim 1 wherein at least one ofthe subarray circuit units is formed on a routing substrate forconducting electrical signals between the integrated circuits in thesubarray circuit unit and providing input/output signal connections tothe subarray circuit unit.
 6. The system of claim 5 wherein the routingsubstrate includes conductive through vias for providing signals betweeneach circuit unit and individual elements in the transducer array. 7.The system of claim 1 wherein all of the subarray circuit units arepositioned in a hand-held probe unit.
 8. The system of claim 1 whereinthe first integrated circuit in each circuit unit includes wiringpatterns and bond wires for conducting electrical signals between thefirst and second integrated circuits in the circuit unit and providinginput/output signal connections for the subarray circuit unit.
 9. Thesystem of claim 8 including a third integrated circuit and additionalbond wires extending from bond pads on the first integrated circuit toeffect connections between the second and third integrated circuits. 10.The system of claim 1 wherein the second plane is positioned between thefirst and third planes and the first integrated circuit, includesconductive through vias for providing signals between each circuit unitand individual elements in the transducer array.
 11. An ultrasoundimaging system including a transducer array probe unit and a systemconsole for processing and displaying image data, the probe unitcomprising: an array of transducer elements arranged along a plane; aplurality of subarray circuit units each comprising a plurality ofintegrated circuits formed over one another in a stacked configuration,each circuit unit connected to multiple ones of the transducer elements;a multi-wiring unit providing electrical connections between transducerelements and circuit units and providing input/output signal connectionsbetween at least the one circuit unit and the system console; and aplurality of removable clamps, each clamp providing connections betweenone or more flexible circuits and the circuit board, wherein a first ofthe integrated circuits is positioned in a first plane and a second ofthe integrated circuits is positioned in a second plane parallel withthe first plane, with the first integrated circuit including a pluralityof bond pads formed along a surface thereof, with the circuit unitincluding bond wires extending from some of the bond pads on the firstintegrated circuit to the second circuit to provide connections betweenthe first and second integrated circuits.
 12. The system of claim 11wherein the transducer elements are each taken from the group consistingof a lead zirconate titanate transducer (PZT), a capacitiveMicromachined Ultrasonic Transducer (cMUT), a piezoelectricMicromachined Ultrasonic Transducer (pMUT), and a PolyVinylidineDiFluoride (PVDF) transducer.
 13. The probe of claim 11 furtherincluding a third integrated circuit positioned in a plane parallel withthe second plane, with the first integrated circuit including bond padsconnected with bond wires to provide connections between the second andthird integrated circuits.
 14. The system of claim 11 wherein eachcircuit unit is a multi-chip module having a controller integratedcircuit formed over a receiver integrated circuit formed over atransmitter integrated circuit, the transmitter integrated circuitproviding signal routing between the controller integrated circuit andthe receiver integrated circuit in each subarray circuit unit.
 15. Thesystem of claim 11 wherein the multi-wiring unit includes multipleflexible circuit boards and multiple printed circuit boards with eachcircuit unit mounted on one of the printed circuit boards withelectrical connection through the one of the printed circuit boards andthrough electrically conductive through-flex vias in one of the flexiblecircuit boards to effect connection with the transducer elements.
 16. Anultrasound imaging system of the type having a probe unit and a systemconsole connected to the probe unit through a cable, the systemcomprising: a plurality of transducer elements; a plurality of circuitunits, each connected to multiple ones of the transducer elements,circuitry in each unit comprising a plurality of integrated circuits,with at least a first of the integrated circuits formed over a second ofthe integrated circuits in a stacked configuration; and a plurality ofcircuit board structures providing electrical connections between thetransducer elements and the circuit units, with, for at least one of thecircuit units, the first integrated circuit including a first pluralityof first bond pads along a surface thereof and the second integratedcircuit including a second plurality of second bond pads along a surfacethereof, bond wires extending between pairs of first and second bondpads to provide input/output signal connections therebetween.
 17. Theultrasound imaging system of claim 16 wherein each circuit unit includesat least three integrated circuits with one of the first integratedcircuits comprising transmission circuitry for generating the acousticsignals, one of the integrated circuits comprising receiver circuitryfor processing of the reflected signals and one of the integratedcircuits comprising control circuitry for pulse timing.
 18. Theultrasound imaging system of claim 16 wherein the plurality of circuitunits and the plurality of circuit board structures are positioned inthe probe unit.
 19. The ultrasound imaging system of claim 16 wherein atleast some of the plurality of circuit units are positioned in thesystem console.
 20. The ultrasound imaging system of claim 18 includinga third integrated circuit and additional bond wires extending from bondpads on the first integrated circuit to effect connections between thesecond and third integrated circuits.
 21. The system of claim 16 whereinthe transducer elements are arranged in rows and columns and are formedin adjoining subarrays such that each circuit unit is a subarray circuitunit connected to a subarray of the transducer elements.
 22. The systemof claim 11 wherein the transducer elements are formed in a matrix ofsubarrays with each subarray containing a plurality of the transducerelements and with each of the circuit units of integrated circuitsconnected to one of the sub arrays of transducer elements, and whereinthe multi-wiring unit provides electrical connections between subarraysof the transducer elements and subarrays of the circuit units.